Are you trying to rank the users ?
Typically profile pages tend to be low quality so can be wise to noindex them because of there little value. Your case maybe different but thats the general rule.

As for duplicate content, there is no penalty for this, often its more of a case of missed opportunity

Thank you for your reply. It's good to know that it is not considered duplicate content.

And you are right, the user profiles are pretty low in quality. I did not think to noindex them.. That's a good idea because I have to remove users on a regular basis and this leads to 404s, which from what i heard Google doesn't really like. Plus the title, meta, etc. are pretty standard which does lead to duplicate content.

deleted user profiles are a good case to catch there is no user and display a friendly page informing the user the profile no longer exists.
I say this because if your site contains user generated content like a forum and you dont remove the content then you can be generating the 404 pages yourself internally. Its a cleaner and user friendly method of handling that situation.

As for 404's and google. I have heard google say many times, they understand the internet is broken, that statement always makes me smile. so they expect 404 errors but I tend to think its good house keeping to keep errors such as this to a minimum as it shows the site is well maintained. Plus it never nice for a user to stumble across a 404.

Adding to this

Originally Posted by webmasterpath

Thank you for your reply. It's good to know that it is not considered duplicate content.

And you are right, the user profiles are pretty low in quality. I did not think to noindex them.. That's a good idea because I have to remove users on a regular basis and this leads to 404s, which from what i heard Google doesn't really like. Plus the title, meta, etc. are pretty standard which does lead to duplicate content.

I really appreciate your advice. Thank you

I followed your advice and added noindex/nofollow to the user profiles and also added the main directory path (as they are all listed on a main template) to the robots file. Ran another sitemap generator and now the sitemap is much smaller, cleaner and about 95% of the URLs submitted where indexed by Google. So it appears that this was a great suggestion and again I really appreciate your advice on it.

You are correct, user profiles generally do not have much quality and I was running into a problem with duplicate content because the title, keywords and meta description where the same for all profiles (only the user's name at the start was different). So this also helped with duplicate content.

However now I am considering taking the top users (this is an eCommerce website) and creating URL friendly and SEO optimized pages that will be added to the sitemap and I will try to rank for. For example a user (Mark) is a top seller on the site. So I will create a page and original article with H1/H2/H3, alt tags, custom title, meta, keywords and URL friendly link that contains the keyword(s) I want to rank for this user. It's a bit of a chore because I wil do this manually for around 100 top profiles, but it will add unique content to the site and have all of the things that Google appears to want.

Providing the new pages can be found via links on your site there is no need to add them to a site map. Google follow links really well so its quite a miss conception that adding them to a site map helps. Its possible it may speed up google finding them but not in every case.
If the pages are orphaned pages or are the result of a search then of course there is no way of google finding them so a site map then is required.